"The best chart on this is the so-called "parfait chart" by the Center on Budget and Policy Priorities (CBPP), which breaks down what specific policies caused the big increase in the U.S. federal debt in the 2000s. Strikingly, the current debt was almost entirely caused by events in the past 13 years. The most important factor was the Bush tax cuts of 2001 and 2003, which greatly reduced federal revenues and put the federal government into deficit after the surpluses of the late '90s and early '00s, but the economic downturn, the stimulus and other recovery measures, and the wars in Iraq and Afghanistan all played important roles too. "